Laser welding has high energy density and can be performed in a narrow heat-affected zone at a high speed. However, when there is a gap on a welding object, there is a concern that a laser beam will leak from the gap, which makes it difficult to perform welding. In order to solve this problem, many hybrid welding methods using consumable-electrode-type arc welding have been proposed.
For example, FIG. 13 is a block diagram illustrating the structure of a hybrid welding apparatus according to the related art. Laser generating unit 1 includes laser oscillator 2, laser transmitting unit 3, and focusing optical system 4. Focusing optical system 4 radiates laser beam 5 to the welding position of welding object 6. For example, an optical fiber or a combination of lenses is used as laser transmitting unit 3. Focusing optical system 4 includes one lens or a plurality of lenses. Wire 7 is fed to the welding position of welding object 6 through torch 9 by wire feeding unit 8. Arc generating unit 10 controls wire feeding unit 8. Arc generating unit 10 controls the wire feeding unit to feed wire 7 to the welding position of welding object 6 through torch 9 such that welding arc 11 is generated or stops between wire 7 and welding object 6. Control unit 12 controls laser generating unit 1 and arc generating unit 10. Although not shown in the drawings, laser oscillator 2 outputs a predetermined output value. In addition, laser oscillator 2 receives a signal of the output value set by control unit 12 and outputs a laser beam corresponding to the signal. Similar to laser generating unit 1, the output of arc generating unit 10 is controlled by control unit 12.
The operation of the hybrid welding apparatus having the above-mentioned structure according to the related art will be described below. When welding starts, although not shown in the drawings, control unit 12 receiving a welding start command transmits a laser welding start signal to laser generating unit 1 to start the radiation of laser beam 5. In addition, control unit 12 transmits an arc welding start signal to arc generating unit 10 to start arc discharge. In this way, welding starts. When welding ends, control unit 12 receiving a welding end command transmits a laser welding end signal to laser generating unit 1 to end the radiation of laser beam 5. In addition, control unit 12 transmits an arc welding end signal to arc generating unit 10 to end arc discharge. In this way, welding ends.
Various improvements of the above-mentioned hybrid welding method have been proposed. For example, PTL 1 discloses a technique in which the gap between laser radiation and arc discharge is set to a predetermined value at which arc does not interfere with laser, thereby improving the melting rate of a welding object. In the above-mentioned case, the laser beam does not directly irradiate to the wire and a welding current is almost used for arc welding. NPL 1 discloses a technique in which the size of a molten pool is substantially determined by the size of the molten pool formed by arc welding.
PTL 2 discloses a technique that radiates the laser beam to the wire to reduce the arc current and the size of the molten pool formed by arc welding. PTL 3 discloses a technique in which pulsed arc welding is used as arc welding and the pulse frequency of pulsed arc welding is controlled according to a laser-wire distance at the radiation point of the welding object, thereby improving the gap tolerance.
However, the related art does not disclose a hybrid welding method and a hybrid welding apparatus having all of the above-mentioned advantages. That is, in the related art, it is difficult to reduce arc energy or arc current required to melt the wire and reduce the size of the molten pool formed by welding arc. In addition, it is difficult to prevent the generation of spatter involving the rapid evaporation of a molten droplet formed at the end of the wire. It is also difficult to supply a high laser output to the welding position to obtain a high welding rate.
[PTL 1] Japanese Patent Unexamined Publication No. 2002-346777
[PTL 2] Japanese Patent Unexamined Publication No. 2008-93718
[PTL 3] Japanese Patent Unexamined Publication No. 2008-229631
[NPL 1] Seiji Katayama, Satoru Uchiumi, Masami Mizutani, Jing-Bo Wang, Koji Fujii, Penetration Characteristics and Porosity Prevention Mechanism in YAG Laser-MIG Hybrid Welding of Aluminum Alloy, Light Metal Welding, 44, 3 (2006)